1. Field of the Invention
This invention patent relates to an apparatus and method of making a paper end for a rigid cylindrical or shaped container. More particularly, this invention relates to an apparatus and method of making a pressed paper end that minimizes or eliminates wrinkles, waves and other deformations in the paper end chuck wall.
2. Description of the Related Art
Rigid cylindrical and shaped composite containers used to package goods such as snacks and other food items are an important product in the packaging industry. These containers usually are manufactured with open ends, one of which may be closed with a metal, plastic or paper bottom closure. The top end may be sealed with a paper or composite end that is adhered to the container top rim but that can be easily removed by the consumer.
There are three basic types of paper ends for use in sealing rigid composite containers. The first type is a stiff paper disc that often is fitted within an internal groove near the bottom of the container. The bottom rim below the groove may be serrated and then curled inward against the inside surface of the container and glued thereto to help hold the paper end in place. Examples of this type of closure can be found on containers for dry food products such as bread crumbs and stuffing.
The second type of paper end is a cup-shaped structure having a central panel and a skirt. This second type of paper closure typically is made by cutting paperboard into a circular blank and then using an annular ring device to simultaneously insert the blank into the open bottom end of a container while forming the closure into a cup shape. The resulting container will have a recessed bottom, and the container body (bottom rim) may be curled inwardly around the paper end skirt.
The third type of paper end, which is the subject of the present invention, is a stamped paper end which has been pre-formed by a die press similar to those used to make metal ends. Like the second type of paper end, stamped paper ends typically have a flat central panel and an annular (circumferential) skirt, referred to as a chuck wall. The chuck wall abuts the inner surface of the container body when the paper end is inserted into a container.
To make a stamped (or pressed) paper end, flat paperboard material is fed into a die press (a.k.a. stamping press) and then compressed between upper and lower opposing dies. In standard die presses (like the kind used to form metal ends), the chuck wall is created by forming/stretching the paper material along two areas of compression on either side of the chuck wall while the chuck wall itself is relatively unsupported.
The problem with this forming method is that it can create wrinkles, waves or other deformations in the chuck wall. Deformations in the chuck wall area are particularly troublesome because, when the pre-formed (pressed) paper end is inserted into the container body, these deformations can interfere with the proper sealing of the container.
A further problem can arise when pressed paper ends are installed onto a container. Inserting the end into the container can create a pressure seal so air inside the container cannot escape. As soon as the sealed container is ejected from the seal head, this excess internal pressure can put stress on the still hot, malleable paper end and thermo-polymer sealant, resulting in an undesirable domed appearance or, worse, a weak or failed end seal.
Another problem can occur when the end of the container near the paper end is squeezed or otherwise compressed. These compression forces can create stress on the paper end, which can result in deformation or failure of the seal.
Yet another problem can occur when containers with pressed paper ends are exposed to lower ambient pressures (such as can occur when the containers are transported across high elevations). Under these conditions the pressure inside the container can cause the paper end to deform outwardly.
Thus there is a need for an improved apparatus and method of forming a pressed paper end that eliminates tears, wrinkles, waves or other deformations in the chuck wall of the paper end when the paper ends are formed.
There is also a need for a method of forming a paper end that allows for the formation of venting channels in the chuck wall area so air inside the container can be released during the end closure insertion process or during exposure to lower ambient pressures.
There is also a need for a paper end closure that allows the container at the end/body interface to compress and absorb shocks near the paper end without destroying the seal.
There is also a need for a paper end that can be vented if the pressure inside the container becomes too great relative to the ambient (outside) pressure.
Further and additional objects will appear from the description, accompanying drawings, and appended claims.